High power converter architecture

ABSTRACT

The power converter is an integration of three topologies which include a forward converter topology, a flyback converter topology, and a resonant circuit topology. The combination of these three topologies functions to transfer energy using three different modes. A first mode, or forward mode, is a forward energy transfer that forwards energy from the input supply to the output load in a manner similar to a forward converter. A second mode, or flyback mode, stores and releases energy in a manner similar to a flyback converter. A third mode, or resonant mode, stores and releases energy from the resonant tank using a resonant circuit and a secondary side forward-type converter topologies. An output circuit of the power converter is configured as a forward-type converter including two diodes and an inductor. The output circuit is coupled to a secondary winding of a converter transformer.

FIELD OF THE INVENTION

The present invention is generally directed to the field of powerconverters. More specifically, the present invention is directed to anew power converter architecture having increased efficiency.

BACKGROUND OF THE INVENTION

There are several power converter topologies that have been developedover the years, which are intended to improve the power density andswitching efficiency of power converters. An emerging focus of newconverter topologies is to provide a means to reduce or eliminateconverter switching losses, while increasing the switching frequencies.Lower loss and higher switching frequency means more efficientconverters, which can reduce the size and weight of convertercomponents. Additionally, with the introduction of high speed compositesemiconductor switches, such as metal oxide semiconductor field effecttransistor (MOSFET) switches operated by pulse width modulation (PWM),recent forward and flyback topologies are now capable of operation atgreatly increased switching frequencies, such as, for example, up to 1.0MHz.

However, an increase in switching frequency can cause a correspondingincrease in switching and component stress related losses, as well asincreased electromagnetic interference (EMI), noise, and switchingcommutation problems, due to the rapid ON/OFF switching of thesemiconductor switches at high voltage and/or high current levels.Moreover, modern electronic components are expected to perform multiplefunctions, in a small space, efficiently, and with few undesirable sideeffects. For instance, a modern voltage converter that provides forrelatively high power density and high switching frequencies, shouldalso include uncluttered circuit topologies, provide for isolation ofthe output or “load” voltage from the input or “source” voltage, andalso provide for variable step-up or step-down voltage transformation.

FIG. 1 illustrates a conventional flyback type voltage converter. Theconverter 10 includes a transistor T1, a controller 14, a transformer12, a capacitor C1, and a diode D1. Input voltage to the circuit may beunregulated DC voltage derived from an AC supply after rectification andfiltering. The transistor T1 is a fast-switching device, such as aMOSFET, the switching of which is controlled by a fast dynamiccontroller 14 to maintain a desired output voltage Vout. The secondarywinding voltage is rectified and filtered using the diode D1 and thecapacitor C1. The transformer 12 of the flyback converter functionsdifferently than a typical transformer. Under load, the primary andsecondary windings of a typical transformer conduct simultaneously.However, in the flyback converter, the primary and secondary windings ofthe transformer do not carry current simultaneously. In operation, whenthe transistor T1 is turned ON, the primary winding of the transformer12 is connected to the input supply voltage such that the input supplyvoltage appears across the primary winding, resulting in an increase ofmagnetic flux in the transformer 12 and the primary winding currentrises linearly. However, with the transistor T1 turned ON, the diode D1is reverse biased and there is no current through the secondary winding.Even though the secondary winding does not conduct current while thetransistor T1 is turned ON, the load, represented as resistor Rload,coupled to the capacitor C1 receives uninterrupted current due topreviously stored charge on the capacitor.

When the transistor T1 is turned OFF, the primary winding current pathis broken and the voltage polarities across the primary and secondarywindings reverse, making the diode D1 forward biased. As such, theprimary winding current is interrupted but the secondary winding beginsconducting current thereby transferring energy from the magnetic fieldof the transformer to the output of the converter. This energy transferincludes charging the capacitor C1 and delivery energy to the load. Ifthe OFF period of the transistor T1 is sufficiently long, the secondarycurrent has sufficient time to decay to zero and the magnetic fieldenergy stored in the transformer 12 is completely dissipated.

The flyback topology has long been attractive because of its relativesimplicity when compared with other topologies used in low powerapplication. The flyback “transformer” serves the dual purpose ofproviding energy storage as well as converter isolation, theoreticallyminimizing the magnetic component count when compared with, for example,the forward converter. A drawback to use of the flyback is therelatively high voltage and current stress suffered by the switchingcomponents. Additionally, high turn-off voltage (caused by the parasiticoscillation between transformer leakage inductance and switchcapacitance) seen by the primary switch traditionally requires the useof a resistor, capacitor, diode subcircuit, such as a snubber circuit.This parasitic oscillation is extremely rich in harmonics and pollutesthe environment with EMI, and causes high switching losses from theswitching components in the form of extra thermal dissipation.

FIG. 2 illustrates a conventional forward type voltage converter. Theconverter 20 includes a transistor T1, a controller 24, a transformer22, a capacitor C1, diodes D1 and D2, and an inductor L1. As with theflyback converter, input voltage to the circuit may be unregulated DCvoltage derived from an AC supply after rectification and filtering. Thetransistor T1 is a fast-switching device, such as a MOSFET, theswitching of which is controlled by a fast dynamic controller 24 tomaintain a desired output voltage Vout. The secondary winding voltage isrectified and filtered using the diode D1 and the capacitor C1. Theload, represented as resistor Rload, is coupled across the rectifiedoutput of the secondary winding. The transformer 22 is desired to be anideal transformer with no leakages, zero magnetizing current, and nolosses. In operation, when the transistor T1 is turned ON, the primarywinding of the transformer 22 is connected to the input supply voltagesuch that the input supply voltage appears across the primary windingand simultaneously a scaled voltage appears across the secondarywinding. The diode D1 is forward biased when the transistor T1 is turnedON, and the scaled voltage across the secondary winding is applied tothe low pass filter circuit preceding the load. The diode D2 is reversebiased and therefore does not conduct current when the transistor T1 isturned ON. In the case of an ideal transformer, no energy is stored inthe transformer, unlike the flyback converter. The scaled voltage issupplied as a constant output voltage when the transistor T1 is turnedON.

When the transistor T1 is turned OFF, the primary winding current pathis broken and the voltage polarities across the primary and secondarywindings reverse, making the diode D1 reversed biased and the diode D2forward biased. The result is zero current flow through both the primaryand secondary windings. However, the forward biased diode D2 provides afreewheeling path for uninterrupted current to continue to flow throughthe inductor L1 and the load. The inductor L1 provides the magnetic fluxto maintain this current flow while the transistor T1 is turned OFF.When the transistor T1 is turned OFF, there is no power flow from theinput source to the load, but the output voltage is maintained nearlyconstant by a relatively large capacitor C1. The charged capacitor C1and the inductor L1 provide continuity in load voltage. However, sincethere is no input power when the transistor T1 is turned OFF, the storedenergy in the capacitor C1 and the inductor L1 slowly dissipate. Theswitching frequency of the transistor T1 is set to maintain the outputvoltage within a required tolerance.

As with the flyback converter, the non-ideal nature of the forwardconverter results in noise and loses that reduce efficiency.

In an effort to reduce or eliminate the switching losses and reduce EMInoise the use of “resonant” or “soft” switching techniques has beenincreasingly employed in the art. The application of resonant switchingtechniques to conventional power converter topologies offers manyadvantages for high density, and high frequency, to reduce or eliminateswitching stress and reduce EMI. Resonant switching techniques generallyinclude an inductor-capacitor (LC) subcircuit in series with asemiconductor switch which, when turned ON, creates a resonatingsubcircuit within the converter. Further, timing the ON/OFF controlcycles of the resonant switch to correspond with particular voltage andcurrent conditions across respective converter components during theswitching cycle allows for switching under zero voltage and/or zerocurrent conditions. Zero voltage switching (ZVS) and/or zero currentswitching (ZCS) inherently reduces or eliminates many frequency relatedswitching losses.

The application of such resonant switching techniques to conventionalpower converter topologies offers many advantages for high density, highfrequency converters, such as quasi sinusoidal current waveforms,reduced or eliminated switching stresses on the electrical components ofthe converter, reduced frequency dependent losses, and/or reduced EMI.However, energy losses incurred during control of zero voltage switchingand/or zero current switching, and losses incurred during driving, andcontrolling the resonance means, are still problematic.

Several power converter topologies have been developed utilizingresonant switching techniques, for example U.S. Pat. No. 7,764,515entitled “Two Terminals Quasi Resonant Tank Circuit,” to Jansen et al.(Jansen), which is hereby incorporated in its entirety by reference.Jansen is directed to a flyback type converter including aquasi-resonant tank circuit. FIG. 3 illustrates the flyback typeconverter of Jansen. The quasi-resonant flyback converter 30 is similarto the flyback converter 10 of FIG. 1 with the addition of a quasiresonant tank circuit formed by a transistor T2, diodes D2, D3, and D4,and capacitors C2 and C3. When the transistor T1 is turned ON, thetransistor T2 is turned OFF, and the primary winding of the transformer32 is connected to the input supply voltage such that the input supplyvoltage appears across the primary winding, resulting in an increase ofmagnetic flux in the transformer 32 and the primary winding currentrises linearly. No current flows through the secondary winding of thetransformer 32 because the diode D1 is reverse biased. When thetransistor T1 is turned OFF, the transistor T2 turns ON parametrically,without control of a separate control circuit. The diodes D2, D3, and D4and the capacitor C3 function as driving circuitry for the transistorT2. With the transistor T2 turned ON, the capacitor C2 is essentiallycoupled in parallel to the transformer 32, and the energy previouslystored in the primary winding causes current to circulate in the circuitformed by the capacitor C2 and the primary winding, forming a resonanttank. As with the flyback converter of FIG. 1, energy stored in theprimary winding is delivered to the load while the transistor T1 isturned OFF. However, in the quasi-resonant flyback converter 30 of FIG.3, a portion of the resonant energy generated in the resonant tank isalso delivered to the load while the transistor T1 is turned OFF and thetransistor T2 is turned ON. In this manner, the quasi-resonant flybackconverter 30 of FIG. 3 delivers peak energy equal to energy from thetypical flyback operation plus the resonant energy. However, currentflow within the resonant tank cycles between positive and negativecurrent flow through the primary winding. The configuration of thesecondary side circuit, in particular the diode D1, only allows deliveryof resonant energy during one direction of primary winding current flow.Resonant energy corresponding to the other direction of primary currentflow is not delivered.

In addition to providing an increase in peak energy, the quasi-resonantflyback converter of FIG. 3 provides the conventional advantagesassociated with a resonant circuit, such as reduced frequency dependentlosses and EMI. However, the increased energy delivered by thequasi-resonant flyback converter is still less than the energy deliveredby the forward converter.

SUMMARY OF THE INVENTION

The power converter is an integration of three topologies which includea forward converter topology, a flyback converter topology, and aresonant circuit topology. The combination of these three topologiesfunctions to transfer energy in three different modes. A first mode, orforward mode, is a forward energy transfer that forwards energy from theinput supply to the output load in a manner similar to a forwardconverter. A second mode, or flyback mode, stores and releases energy ina manner similar to a flyback converter. A third mode, or resonant mode,stores and releases energy from a resonant tank using the resonantcircuit and secondary side forward-type converter topologies. An outputcircuit of the power converter is configured as a forward-type converterincluding two diodes and an inductor. The output circuit is coupled to asecondary winding of a converter transformer.

In an aspect, a power converter circuit includes a transformer, anoutput circuit, a primary switch, a resonant circuit, and a controller.The transformer has a primary winding coupled to an input supply voltageand a secondary winding. The output circuit is coupled to the secondarywinding, wherein the output circuit includes a first diode, a seconddiode, an inductor, and a capacitor. The first diode and the seconddiode are coupled to the secondary winding of the transformer such thatwhen the first diode is forward biased, the second diode is reversebiased, and when the first diode is reverse biased, the second diode isforward biased. The primary switch is coupled in series to the primarywinding. The resonant circuit is coupled in parallel to the primarywinding, wherein the resonant circuit includes an auxiliary switch and aresonant tank. The controller is coupled to the primary switch. Thepower converter circuit is configured to forward energy from the inputsupply voltage to the output circuit, to store energy from leakageinductance, magnetizing inductance, and parasitic capacitances asresonant energy in the resonant tank, and to deliver the stored resonantenergy to the output circuit.

In some embodiments, the power converter circuit is configured toforward energy from the input supply voltage to the output circuit whenthe primary switch is ON. In some embodiments, the parasiticcapacitances include parasitic capacitances from the auxiliary switchand the primary switch. In some embodiments, the resonant energy isdelivered over an entire resonant cycle of the resonant tank, whereinthe resonant tank includes the primary winding and the resonant cycleincludes a positive primary winding current flow and a negative primarywinding current flow. In some embodiments, energy delivered to theoutput load includes a summation of energy forwarded from the inputsupply, resonant energy stored and released by the resonant tank, andparasitic capacitances and leakage inductance stored and released asadditional resonant energy by the resonant tank. In some embodiments,the auxiliary switch is a parametrically controlled auxiliary switch. Insome embodiments, the power converter circuit also includes drivingcircuitry coupled to the auxiliary switch and to the primary switch,wherein the driving circuitry is configured to parametrically controlthe auxiliary switch according to a voltage condition of the primaryswitch. In some embodiments, the resonant circuit, the transformer, andthe output circuit are configured to store and release the resonantenergy and the additional resonant energy according to a flyback mode ofenergy conversion. In some embodiments, during the flyback mode ofenergy conversion, the primary switch is OFF. In some embodiments, ananode of the first diode is coupled to a first terminal of the secondarywinding, an anode of the second diode is coupled to a second terminal ofthe secondary winding, a cathode of the first diode and a cathode of thesecond diode are each coupled to a first terminal of the inductor, and asecond terminal of the inductor is coupled to the capacitor. In someembodiments, a primary winding current rises linearly to a peak valuewhen the primary switch is ON.

In another aspect, a power converter circuit includes a transformer, anoutput circuit, a primary switch, a resonant circuit, driving circuitry,and a controller. The transformer has a primary winding coupled to aninput supply voltage and a secondary winding. The output circuit iscoupled to the secondary winding. The output circuit includes a firstdiode, a second diode, an inductor, and a capacitor. The first diode andthe second diode are coupled to the secondary winding of the transformersuch that when the first diode is forward biased, the second diode isreverse biased, and when the first diode is reverse biased, the seconddiode is forward biased. The primary switch is coupled in series to theprimary winding. The resonant circuit is coupled in parallel to theprimary winding, wherein the resonant circuit includes an auxiliaryswitch and a resonant tank. The driving circuitry is coupled to theauxiliary switch and to the primary switch. The driving circuitry isconfigured to parametrically control the auxiliary switch according to avoltage condition of the primary switch. The controller is coupled tothe primary switch. The power converter circuit is configured to forwardenergy from the input supply voltage to the output circuit, to storeenergy from leakage inductance, magnetizing inductance, and parasiticcapacitances as resonant energy in the resonant tank, and to deliver thestored resonant energy to the output circuit. In some embodiments, ananode of the first diode is coupled to a first terminal of the secondarywinding, an anode of the second diode is coupled to a second terminal ofthe secondary winding, a cathode of the first diode and a cathode of thesecond diode are each coupled to a first terminal of the inductor, and asecond terminal of the inductor is coupled to the capacitor.

In yet another aspect, a method of transferring energy using a powerconverter is disclosed. The method includes configuring a powerconverter. The power converter includes a transformer having a primarywinding coupled to an input supply voltage and a secondary winding, anoutput circuit having an inductor coupled to the secondary winding, anda primary switch coupled in series to the primary windings. The methodalso includes forwarding energy from the input supply voltage to theoutput circuit while the primary switch is ON. The method also includesI.forming a resonant tank including the primary winding when the primaryswitch is OFF, wherein the resonant tank includes resonant energyderived from stored magnetizing inductance, stored leakage inductanceand parasitic capacitances. The method also includes delivering theresonant energy in the resonant tank to the output circuit while theprimary switch is OFF.

In some embodiments, energy is continuously transferred from a primaryside of the power converter to the output circuit while the primaryswitch is both ON and OFF. In some embodiments, the parasiticcapacitances include parasitic capacitances from the auxiliary switchand the primary switch. In some embodiments, the resonant energy isdelivered over an entire resonant cycle of the resonant tank, whereinthe resonant tank includes the primary winding and the resonant cycleincludes a positive primary winding current flow and a negative primarywinding current flow. In some embodiments, energy delivered to theoutput load includes a summation of energy forwarded from the inputsupply, resonant energy stored and released by the resonant tank, andparasitic capacitances and leakage inductance stored and released asadditional resonant energy by the resonant tank. In some embodiments,the method also includes controlling the auxiliary switch throughself-commutation. In some embodiments, the auxiliary switch turns ON andOFF according to a voltage condition of the primary switch. In someembodiments, the resonant energy is stored and delivered according to aflyback mode of energy conversion. In some embodiments, during theflyback mode of energy conversion, the primary switch is OFF. In someembodiments, the output circuit includes a first diode, a second diode,and a capacitor, wherein the first diode and the second diode arecoupled to the secondary winding of the transformer such that when thefirst diode is forward biased, the second diode is reverse biased, andwhen the first diode is reverse biased, the second diode is forwardbiased. In some embodiments, a primary winding current rises linearly toa peak value when the primary switch is ON.

BRIEF DESCRIPTION OF THE DRAWINGS

Several example embodiments are described with reference to thedrawings, wherein like components are provided with like referencenumerals. The example embodiments are intended to illustrate, but not tolimit, the invention. The drawings include the following figures:

FIG. 1 illustrates a conventional flyback type voltage converter.

FIG. 2 illustrates a conventional forward type voltage converter.

FIG. 3 illustrates the flyback type converter of Jansen.

FIG. 4 illustrates a power converter according to an embodiment.

FIG. 5 illustrates a conceptualized version of the power convertercircuit of FIG. 4.

FIG. 6 illustrates exemplary voltage and current waveforms correspondingto operation of the power converter of FIG. 4.

FIG. 7 illustrates a power converter according to another embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present application are directed to a powerconverter. Those of ordinary skill in the art will realize that thefollowing detailed description of the power converter is illustrativeonly and is not intended to be in any way limiting. Other embodiments ofthe power converter will readily suggest themselves to such skilledpersons having the benefit of this disclosure.

Reference will now be made in detail to implementations of the powerconverter as illustrated in the accompanying drawings. The samereference indicators will be used throughout the drawings and thefollowing detailed description to refer to the same or like parts. Inthe interest of clarity, not all of the routine features of theimplementations described herein are shown and described. It will, ofcourse, be appreciated that in the development of any such actualimplementation, numerous implementation-specific decisions must be madein order to achieve the developer's specific goals, such as compliancewith application and business related constraints, and that thesespecific goals will vary from one implementation to another and from onedeveloper to another. Moreover, it will be appreciated that such adevelopment effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skill in the art having the benefit of this disclosure.

FIG. 4 illustrates a power converter according to an embodiment. Thepower converter 40 is configured to receive an unregulated DC voltagesignal at an input node Vin and to provide a regulated output voltageVout. Input voltage to the circuit may be unregulated DC voltage derivedfrom an AC supply after rectification. The input voltage is typicallyfiltered, such as via capacitor 60. In some embodiments, the outputvoltage level is suitable for many low voltage appliances such ascomputer laptops, cell phones and other hand held devices. In anexemplary embodiment the output voltage Vout can be set within the range5-40 VDC. Alternatively, the power converter 100 can provide the outputvoltage Vout that is less than 5 VDC. In other embodiments, the outputvoltage level is suitable for high power applications greater than 40VDC.

The power converter 40 includes power conversion and resonant circuitry.In some embodiments, the power converter is configured to includeattributes from a flyback converter and a forward converter to performpower conversion. In general, the power converter can includeconfigurations of switch mode power supplies known to a person of skillin the art. Additionally, the power converter includes a resonant tankand is configured to delivery resonant energy to a load. The powerconverter 40 includes a primary switch 48, an auxiliary switch 46, acontroller 44, a transformer 42, and a capacitor 50. The primary switch48 is coupled in series with a primary winding of the transformer 42.The auxiliary switch 46 is coupled in series with the capacitor 50, andthe serially coupled auxiliary switch 46 and capacitor 50 are coupled inparallel to the primary winding of the transformer 42.

The primary switch 48 and the auxiliary switch 46 are each a suitableswitching device. In an exemplary embodiment, the primary switch 48 andthe auxiliary switch 46 are each a n-type metal-oxide-semiconductorfield-effect transistor (MOSFET) device. Alternatively, any othersemiconductor switching device known to a person of skill in the art canbe substituted for the primary switch 48 and/or the auxiliary switch 46.The primary switch 48 is controlled by the controller 44. In someembodiments, the controller 44 includes a pulse width modulation (PWM)circuit. The controller 44 regulates the duty cycle of the primaryswitch 48 with the PWM circuit. The controller 44 can sense voltageand/or current conditions within the circuit, such as the voltage and/orcurrent across the sense resistor 70. The controller 44 can include acurrent comparator circuit (not shown) to use with a current feedbackcircuit (not shown) in regulating the duty cycle of the primary switch48. Likewise, the controller 44 can include a voltage comparator circuit(not shown) to use with a voltage feedback circuit (not shown) inregulating the duty cycle of the primary switch 48.

The power converter 40 further includes output circuitry coupled to asecondary winding of the transformer 42 and driving circuitry for theauxiliary switch 46. The output circuitry includes a rectifier diode 62,a rectifier diode 64, and an output capacitor 66. An anode of therectifier diode 62 is coupled to a first terminal of the secondarywinding. A cathode of the rectifier diode 62 is coupled to a firstterminal of the output capacitor 66 and coupled to the output node Vout.An anode of the rectifier diode 64 is coupled to a second terminal ofthe secondary winding. A cathode of the rectifier diode 64 is coupled tothe first terminal of the output capacitor 66 and coupled to the outputnode Vout. The output capacitor 66 is coupled to a Vout node across anoutput load, represented by a resistor 68.

In some embodiments, the driving circuitry for the auxiliary switch 46is configured such that when the voltage across the primary winding ofthe transformer 42 is higher than zero, the auxiliary switch 46 will bein the ON state. The driving circuitry is further configured such thatwhen the voltage across the primary winding of the transformer 42 isequal or lower than zero, the auxiliary switch 46 will be in the OFFstate.

Where the controller 44 employs force commutation for turning ON and OFFof the primary switch 48, adaptive self-commutation is used forswitching the auxiliary switch 46 ON and OFF. In an exemplaryembodiment, the driving circuitry for the auxiliary switch 46 isimplemented using a diode 54, a diode 56, a diode 58, and a capacitor52, as shown in FIG. 4. In an exemplary method of operating the drivingcircuitry of FIG. 4, at the moment that the rising edge of the voltageacross the primary winding of the transformer 42 reaches zero, the bodydiode of the auxiliary switch 46 starts conducting. Also, diode 56starts conducting at this point and starts charging the gate-to-sourceparasitic capacitance of the auxiliary switch 46 through the capacitor52. The further rising voltage across the capacitor 50 is divided by thecapacitor 52 and the addition of the gate-to-source parasiticcapacitance and the gate-to-drain parasitic capacitance of the auxiliaryswitch 46.

When the voltage across the gate-to-source parasitic capacitance of theauxiliary switch 46 reaches the threshold voltage of the auxiliaryswitch 46, the auxiliary switch 46 will turn ON. It is important thatthe ratio between the voltage across capacitor 50 and the maximumvoltage on the gate of the auxiliary switch 46 is chosen to stay withinthe safe operating area of the auxiliary switch 46. The ratio can bedimensioned with the value of the capacitor 52. The gate voltage of theauxiliary switch 46 will remain substantially the same until the voltageacross the capacitor 50 has reduced to the same level of the gatevoltage. When the voltage across the capacitor 50 further reduces, thediode 58 starts conducting and will pull the gate voltage of theauxiliary switch 46 down until it reaches the gate threshold voltage atwhich point the auxiliary switch 46 turns OFF. Diodes 54, 56, and 58further prohibit the voltage across the capacitor 50 to go significantlybelow zero. It is understood that alternatively configured drivingcircuits and alternative methods for operating the driving circuit toparametrically turn the auxiliary switch ON and OFF can be implemented.

A resonant circuit is formed by the capacitors 50 and 52, the diodes 54,56, and 58, the auxiliary switch 46 having the body diode and parasiticcapacitances, and the primary winding of the transformer 42. When theauxiliary switch 46 is turned ON and the primary switch 48 is turnedOFF, the capacitors 50 and 52 and the primary winding of the transformer42 form a resonant tank. The turn-on voltage value for the auxiliaryswitch 46 can depend on the capacitance chosen for the capacitors 50 and52. In this manner, the auxiliary switch 46 is parametrically controlledto turn ON and OFF without direct control of a separate control circuit.

FIG. 4 shows a single inductance element, the primary winding of thetransformer 42. The primary winding represents both a magnetizinginductance element and a leakage inductance element. FIG. 5 illustratesa conceptualized version of the power converter of FIG. 4 showing both amagnetizing inductance element Lmag and a leakage inductance elementLleak.

The power converter is an integration of three topologies which includea forward converter topology, a flyback converter topology, and aresonant circuit topology. The combination of these three topologiesfunctions to transfer energy using three different modes. A first mode,or forward mode, is a forward energy transfer that forwards energy fromthe input supply to the output load in a manner similar to a forwardconverter. A second mode, or flyback mode, stores and releases energy ina manner similar to a flyback converter. A third mode, or resonant mode,stores and releases energy from the resonant tank using the resonantcircuit and secondary side forward-type converter topologies. The modesof energy transfer are controlled using a single control element. In theexemplary embodiment of FIG. 4, the force commutation is implemented bythe controller coupled to the primary switch, and the adaptiveself-commutation is implemented by the parametrically controlledauxiliary switch. The controller controls the primary switch so as toregulate output power. The parametrically controlled auxiliary switchenables power delivery using the flyback mode and the resonant mode.

While the primary switch is ON, energy is both forward transmitted tothe output load and stored in the primary side as magnetizing andleakage inductance. While the primary switch is OFF, stored inductanceand parasitic capacitances form resonant energy in the resonant tankwhich is released to the output load. The configuration of the secondaryside circuit allows for delivery of resonant energy for both directionsof resonant current flow through the primary winding.

FIG. 6 illustrates exemplary voltage and current waveforms correspondingto operation of the power converter 40 of FIG. 4. A waveform 100 showsthe primary current Ipri through the primary winding of the transformer42. A waveform 102 shows the drain-to-source voltage Vds of the primaryswitch 48. A waveform 104 shows the drain-to-source voltage Vds of theauxiliary switch 46.

Operation of the power converter is described in terms of the circuit inFIG. 4 and the waveforms of FIG. 6. At time t1, primary switch 48 is ONand auxiliary switch 46 is OFF. Primary switch 48 ON corresponds to thelow drain-to-source voltage Vds.

From time t1 to t2, the primary switch 48 remains ON and the auxiliaryswitch 46 remains OFF, and the primary current Ipri rises linearlyacross the primary winding resulting in increasing magnetizinginductance within the primary winding.

At time t2, the primary switch 48 turns OFF and the auxiliary switch 46turns ON. In some embodiments, there is a delay between the primaryswitch 48 turning OFF and the auxiliary switch 46 turning ON. This delayis a result of the time for the gate-to-source voltage of the auxiliaryswitch 46 to reach the turn on voltage, this delay is a function of thedriving circuit configuration. The driving circuit functions such thatwhen the voltage differential between the source and the gate of theauxiliary switch 46 reaches the turn on voltage, the auxiliary switch 48turns ON. In this manner, the auxiliary switch 46 functions in aself-commutating mode.

From time t2 to t4, the primary switch 48 remains OFF and the auxiliaryswitch 46 remains ON. The drain-to-source voltage Vds across the primaryswitch 48 eventually dissipates, reaching zero volts, or near zerovolts, at time t4.

At time t4, the primary switch 48 is turned ON using zero voltageswitching or near-zero voltage switching. The controller 44 identifieswhen to turn ON the primary switch 48. In some embodiments, the primaryswitch 48 is turned ON when the energy transfer from the resonant tankis completed, and the voltage across the primary switch 48 is at or nearzero for zero voltage switching. The cycle from time t1 to t4 thenrepeats.

As shown in the waveform diagram of FIG. 6, there is either positive ornegative current through the primary winding, Ipri, except at the zerocrossing points. In contrast, conventional flyback and forwardconverters have zero current through the primary winding when the mainswitch is OFF.

When the primary switch 48 is ON, such as during the time period from t1to t2, energy from the input supply is forward transmitted to the loadresistor 68 via the forward biased diode 64. This energy transfercorresponds to the forward mode. The forward converter topology thatenables the forward mode of energy transfer delivers energy to theoutput load, but the forward converter topology does not include aninductor in the output circuit to store energy. When the primary switch48 is OFF, such as during the time period from time t2 to t4, the powerconverter functions in the flyback mode and the resonant mode. From timet2 to t3, the stored magnetizing inductance generates the diminishingprimary current Ipri. At time t3, the energy from the magnetizinginductance is dissipated and the primary current Ipri is zero. Time t3also corresponds to the high drain-to-source voltage Vds in waveform102. While the auxiliary switch 46 is ON, the capacitor 50 and theprimary winding form a resonant tank. After time t3, the power converterstarts to resonate and generate a sinusoidal primary current from theenergy stored in the resonant tank. The resonant tank functions as abi-directional current circuit. The energy stored in the resonant tankis released to the load resistor 68 via alternating forward biaseddiodes 62 and 64. When the primary current flows counter-clockwise inthe resonant tank, the diode 64 is forward biased and resonant energy isreleased to the load resistor 68 via the forward biased diode 64. Whenthe primary current flows clockwise in the resonant tank, the diode 62is forward biased and resonant energy is released to the load resistor68 via the forward biased diode 62. In this manner, resonant energy isdelivered to the output load during the entire resonant mode cycle ofcounter-clockwise and clockwise primary current flow. In contrast, thepower convert 30 of FIG. 3 can only release resonant energy duringclockwise primary current flow within the resonant tank, whichcorresponds to the diode D1 being forward biased. When the diode D1 isreverse biased, corresponding to counter-clockwise primary current flow,the resonant energy can not be released.

The primary side circuit includes a magnetizing inductance energystorage element and a leakage inductance energy storage element. Asdescribed above, the primary winding can functions as both energystorage elements, or a separate inductor can be added in series to theprimary winding. While the primary switch 48 is ON, most of the energystored in the primary winding is from leakage inductance, and most ofthe energy forwarded is from magnetizing inductance. The resonant tankformed while the primary switch 48 is OFF can be conceptually consideredas two resonant tanks. A first resonant tank is formed by the capacitor50 and the magnetizing inductance energy storage element. A secondresonant tank is formed by the capacitor 50 and the leakage inductanceenergy storage element.

Energy is transferred to the output using the forward mode, such as whenthe primary switch 46 is ON, and the flyback and resonant modes, such aswhen the primary switch is OFF. Energy related to magnetizing inductanceon the primary side that is forwarded to the secondary side while theprimary switch is ON is transferred according to the forward mode.Energy that is stored on the primary side while the primary switch is ONand then forwarded to the secondary side while the primary switch is OFFis transferred according to the flyback mode. Some or all of the energytransferred according to the flyback mode is resonant energy stored inthe resonant tank formed while the primary switch is OFF. Leakageinductances stored in the leakage inductance energy storage element andparasitic capacitances of the main and auxiliary switches result inresonant energy stored in the resonant tank. The resonant energy isforwarded to the secondary side while the primary switch is OFF. In thismanner, the power converter continuously transfers energy, when theprimary switch is ON and OFF.

In some embodiments, the leakage inductance is increased intentionallyso as to store more resonant energy. In some embodiments, a transformeris used in which a portion of the primary and secondary magnetic fieldsare purposely decoupled to generate greater leakage inductance. By wayof example, the conventional flyback converter 10 of FIG. 1 uses atransformer built so as to minimize leakage inductance. In an exemplaryconfiguration, the conventional flyback converter circuit may have 1%leakage of the circuit magnetizing inductance. If the magnetizinginductance is 1 millihenry (mH), the leakage inductance is 10microhenries (uH). In an exemplary implementation of the power converterof the present application, the circuit is designed to have leakageinductance of approximately 200 uH. So what the circuit loses by way ofparasitics is more than made up for in increased energy delivered to theload by way of resonant energy. Care must be taken to not have theparasitic capacitance of the switch be too high or else the switcheswill become over-stressed when it turns ON.

The power converter 40 of FIG. 4 does not include an inductor in thesecondary side output circuit. In alternative embodiments, the powerconverter is modified to include an inductor in the secondary side ofthe output circuit. FIG. 7 illustrates a power converter according toanother embodiment. The power converter 140 includes a primary switch148, an auxiliary switch 146, a controller 144, a transformer 142, and acapacitor 150. The power converter 140 further includes output circuitrycoupled to a secondary winding of the transformer 142 and drivingcircuitry for the auxiliary switch 146. The output circuitry includes arectifier diode 162, a rectifier diode 164, an inductor 172, and anoutput capacitor 166. An anode of the rectifier diode 162 is coupled toa first terminal of the secondary winding. A cathode of the rectifierdiode 162 is coupled to a first terminal of the inductor 172. A secondterminal of the inductor 172 is coupled to the output capacitor 66 andcoupled to the output node Vout. An anode of the rectifier diode 164 iscoupled to a second terminal of the secondary winding. A cathode of therectifier diode 164 is coupled to the first terminal of the inductor172. The output capacitor 166 is coupled to a Vout node across an outputload, represented by a resistor 168. In an exemplary embodiment, thedriving circuitry for the auxiliary switch 146 is implemented using adiode 154, a diode 156, a diode 158, and a capacitor 152, as shown inFIG. 7. The driving circuitry for the auxiliary switch 146 functionssimilarly as the driving circuitry for the auxiliary switch 46 in FIG.4.

The power converter 140 is an integration of three topologies whichinclude a forward converter topology, a flyback converter topology, anda resonant circuit topology. The combination of these three topologiesfunctions to transfer energy using three different modes in a mannersimilar to the power converter 40 described above. However, whereas thepower converter 40 is voltage driven and feeds in voltage (voltage Fed),or a voltage mode of operation, the power converter 140 of FIG. 7 iscurrent driven and feeds in current (current Fed), or a current mode ofoperation.

The present application has been described in terms of specificembodiments incorporating details to facilitate the understanding of theprinciples of construction and operation of the power converter. Many ofthe components shown and described in the various figures can beinterchanged to achieve the results necessary, and this descriptionshould be read to encompass such interchange as well. As such,references herein to specific embodiments and details thereof are notintended to limit the scope of the claims appended hereto. It will beapparent to those skilled in the art that modifications can be made tothe embodiments chosen for illustration without departing from thespirit and scope of the application.

What is claimed is:
 1. A power converter circuit comprising: atransformer having a primary winding coupled to an input power supplyand a secondary winding; an output circuit coupled to the secondarywinding, wherein the output circuit comprises a first diode, a seconddiode, an inductor, and a capacitor, further wherein the first diode andthe second diode are coupled to the secondary winding of the transformersuch that when the first diode is forward biased, the second diode isreverse biased, and when the first diode is reverse biased, the seconddiode is forward biased; a primary switch coupled in series to theprimary winding; a sense resistor coupled in series with the primaryswitch on the opposite side as the primary winding; a resonant circuitincluding an auxiliary switch serially coupled to a tank capacitor thatare together coupled in parallel to the primary winding, wherein whenthe primary switch is OFF the tank capacitor and the primary windingform a resonant tank; and a controller coupled to the primary switch andcoupled to a node between the primary switch and the sense resistor suchthat the controller is able to sense voltage or current conditionswithin the power converter circuit; wherein the power converter circuitis configured to: forward energy from the input power supply to theoutput circuit; store energy from leakage inductance, magnetizinginductance, and parasitic capacitances as resonant energy in theresonant tank; and deliver stored resonant energy to the output circuit.2. The power converter circuit of claim 1 wherein the power convertercircuit is configured to forward energy from the input power supply tothe output circuit when the primary switch is ON.
 3. The power convertercircuit of claim 1 wherein the parasitic capacitances comprise parasiticcapacitances from the auxiliary switch and the primary switch.
 4. Thepower converter circuit of claim 1 wherein the resonant energy isdelivered over an entire resonant cycle of the resonant tank, whereinthe resonant cycle comprises a positive primary winding current flow anda negative primary winding current flow.
 5. The power converter circuitof claim 1 wherein energy delivered to the output circuit comprises asummation of energy forwarded from: the input power supply; resonantenergy stored and released by the resonant tank; and parasiticcapacitances and leakage inductance stored and released as additionalresonant energy by the resonant tank.
 6. The power converter circuit ofclaim 1 wherein the auxiliary switch comprises a parametricallycontrolled auxiliary switch.
 7. The power converter circuit of claim 6further comprising driving circuitry coupled to the auxiliary switch andto the primary switch, wherein the driving circuitry is configured toparametrically control the auxiliary switch according to a voltagecondition of the primary switch.
 8. The power converter circuit of claim1 wherein the resonant circuit, the transformer, and the output circuitare configured to store and release the resonant energy according to aflyback mode of energy conversion.
 9. The power converter circuit ofclaim 8 wherein during the flyback mode of energy conversion, theprimary switch is OFF.
 10. The power converter circuit of claim 1wherein an anode of the first diode is coupled to a first terminal ofthe secondary winding, an anode of the second diode is coupled to asecond terminal of the secondary winding, a cathode of the first diodeand a cathode of the second diode are each coupled to a first terminalof the inductor, and a second terminal of the inductor is coupled to thecapacitor.
 11. The power converter circuit of claim 1 wherein a primarywinding current rises linearly to a peak value when the primary switchis ON.
 12. A power converter circuit comprising: a transformer having aprimary winding coupled to an input power supply and a secondarywinding; an output circuit coupled to the secondary winding, wherein theoutput circuit comprises a first diode, a second diode, an inductor, anda capacitor, further wherein the first diode and the second diode arecoupled to the secondary winding of the transformer such that when thefirst diode is forward biased, the second diode is reverse biased, andwhen the first diode is reverse biased, the second diode is forwardbiased; a primary switch coupled in series to the primary winding; asense resistor coupled in series with the primary switch on the oppositeside as the primary winding; a resonant circuit including an auxiliaryswitch serially coupled to a tank capacitor that are together coupled inparallel to the primary winding, wherein when the primary switch is OFFthe tank capacitor and primary winding form a resonant tank; drivingcircuitry coupled to the auxiliary switch and to the primary switch,wherein the driving circuitry is configured to parametrically controlthe auxiliary switch according to a voltage condition of the primaryswitch; and a controller coupled to the primary switch and coupled to anode between the primary switch and the sense resistor such that thecontroller is able to sense voltage or current conditions within thepower converter circuit; wherein the power converter circuit isconfigured to: forward energy from the input power supply to the outputcircuit; store energy from leakage inductance, magnetizing inductance,and parasitic capacitances as resonant energy in the resonant tank; anddeliver stored resonant energy to the output circuit.
 13. The powerconverter circuit of claim 12 wherein an anode of the first diode iscoupled to a first terminal of the secondary winding, an anode of thesecond diode is coupled to a second terminal of the secondary winding, acathode of the first diode and a cathode of the second diode are eachcoupled to a first terminal of the inductor, and a second terminal ofthe inductor is coupled to the capacitor.
 14. A method of transferringenergy using a power converter, the method comprising: configuring thepower converter comprising a transformer having a primary windingcoupled to an input power supply and a secondary winding, an outputcircuit having an inductor coupled to the secondary winding, and aprimary switch coupled in series between the primary winding and a senseresistor; controlling operation of the primary switch with a controllercoupled to the primary switch based on a sensed voltage or current at anode between the primary switch and the sense resistor to which thecontroller is coupled; forwarding energy from the input power supply tothe output circuit while the primary switch is ON; forming a resonanttank including an auxiliary switch serially coupled to a tank capacitorthat are together coupled in parallel to the primary winding when theprimary switch is OFF, wherein the resonant tank includes resonantenergy derived from stored magnetizing inductance, stored leakageinductance and parasitic capacitances; and delivering the resonantenergy in the resonant tank to the output circuit while the primaryswitch is OFF.
 15. The method of claim 14 wherein energy is continuouslytransferred from a primary side of the power converter to the outputcircuit while the primary switch is both ON and OFF.
 16. The method ofclaim 14 wherein the parasitic capacitances comprise parasiticcapacitances from the auxiliary switch and the primary switch.
 17. Themethod of claim 14 wherein the resonant energy is delivered over anentire resonant cycle of the resonant tank, wherein the resonant tankincludes the primary winding and the resonant cycle comprises a positiveprimary winding current flow and a negative primary winding currentflow.
 18. The method of claim 17 wherein the auxiliary switch turns ONand OFF according to a voltage condition of the primary switch.
 19. Themethod of claim 14 wherein energy delivered to the output circuitcomprises a summation of energy forwarded from: the input power supply;resonant energy stored and released by the resonant tank; and parasiticcapacitances and leakage inductance stored and released as additionalresonant energy by the resonant tank.
 20. The method of claim 14 furthercomprising controlling the auxiliary switch through self-commutation.21. The method of claim 20 wherein during the flyback mode of energyconversion, the primary switch is OFF.
 22. The method of claim 14wherein the resonant energy is stored and delivered according to aflyback mode of energy conversion.
 23. The method of claim 14 whereinthe output circuit comprises a first diode, a second diode, and acapacitor, the first diode and the second diode are coupled to thesecondary winding of the transformer such that when the first diode isforward biased, the second diode is reverse biased, and when the firstdiode is reverse biased, the second diode is forward biased.
 24. Themethod of claim 14 wherein a primary winding current rises linearly to apeak value when the primary switch is ON.